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Geotechnical News • March 2012
WASTE GEOTECHNICS
Challenges with meeting regulatory compliance
in the oil sands industry
Nicholas Beier, Amarebh Sorta, Ward Wilson, David Sego
Introduction
Mining and extraction of oil sands
to produce bitumen has been under-
way in north eastern Alberta for over
five decades. The Canadian oil sands
deposit is home to an estimated 300
billion barrels of recoverable bitumen.
At current and predicted production
rates, oil sands exploitation will con-
tinue long into this century. A typical
oil sand ore deposit is comprised of
bitumen (~12 wt%), sand, silts, clays
(mineral content ~85 wt%) and water
(3-6 wt%). The mineralogy of the clay
component is typically kaolinite (50-
60%) and illite (30-50%) with some
montmorillonite (Beier and Sego,
2007).
The production of bitumen from the
oil sands ore body is based on open
pit mining and a hot water extraction
process. Warm to hot water, steam and
process aids such as caustic (NaOH)
are used to extract the bitumen from
the mineral matrix. The extraction pro-
cess recovers 90-92% of the bitumen
and produces a tailings stream consist-
ing of water sand silt clay and residual
bitumen. Typically, the tailings streams
are discharged at approximately 55
wt% (82 wt% sand and 17 wt% fines
defined as <44 µm) into tailings ponds
to recover water. The coarse fraction of
the tailings slurry is used to construct
perimeter dykes using cell construc-
tion or beach discharge. Some fines are
trapped within the sand matrix of the
beaches during this process (≥50%),
while the remaining fines and water (8
wt% fines) flow into the settling pond
(referred to as thin fine tailings). The
fines slowly settle over a few years
to 30-35 wt% and are referred to as
mature fine tailings (MFT). Further
consolidation of the MFT is extremely
slow (in the order of centuries). The
typical Atterberg limits for a range of
MFT are shown in Figure 1. On aver-
age, approximately 1 m
3
of sand and
0.25 m
3
of MFT have been created for
every barrel of bitumen that has been
produced thus far (Beier and Sego,
2008). This has led to the accumulation
of 800 billion m
3
of MFT (Hyndman
and Sobkowicz, 2010) which requires
long-term storage in fluid containment
structures.
The oil sands industry has developed
methods to deal with this inventory
of MFT. For example, the process of
mixing sand with the MFT, termed
consolidated or composite tailings
(CT), requires a mixture of segregated
sand (from a cyclone underflow), MFT
and a coagulant (gypsum). The CT is
mixed at sand to fines ratios (SFR) of
approximately 4:1 and is not expected
to segregate during transport, discharge
or deposition. However, operational
challenges have hindered the com-
mercial full scale success of CT. The
CT operation must compete for sand
that is also used to provide economi-
cal containment dykes. Additionally,
inconsistent control on the CT slurry
densities and/or the depositional tech-
nique (shear environment) has lead to
segregation of the CT slurries resulting
Figure 1. Plasticity chart of oil sand fine tailings.
